In the air: Researchers at Battelle used off-the-shelf optical telecommunication components to create a faster millimeter-wave device. Two low-frequency laser beams were combined to generate a single 100-gigahertz signal.
Battelle
New millimeter-wave technology sends data at 10 gigabits per second.
There's no shortage of demand for faster wireless, but today's fastest technologies--Wi-Fi, 3G cellular networks, and even the upcoming WiMax--max out at tens or hundreds of megabits per second. So far, no commercial wireless system can beat the raw speed of optical fiber, which can carry tens of gigabits per second.
One way to achieve faster speeds is to harness the millimeter-wavelength frequency of the wireless spectrum, although this usually requires expensive and very complex equipment. Now, engineers at Battelle, a research and development firm based in Columbus, OH, have come up with a simpler way to send data through the air with millimeter-wave technology. Earlier this year, in field tests of a prototype point-to-point system, the team was able to send a 10.6-gigabit-per-second signal between antennas 800 meters apart. And more recently, the researchers demonstrated a 20-gigabit-per-second signal in the lab.
Richard Ridgway, a senior researcher at Battelle, says that the technique could be used to send huge files across college campuses, to quickly set up emergency networks in a disaster, and even to stream uncompressed high-definition video from a computer or set-top box to a display.
Whereas Wi-Fi and cellular networks operate on frequencies of 2.4 to 5.0 gigahertz, millimeter-wave technology exploits a region from about 60 to 100 gigahertz. These waves can carry more data because they oscillate faster. Much of the millimeter region is unlicensed and open for use; it has only been neglected because of the difficulty and expense involved in generating a millimeter-wave signal, encoding information on it, and then decoding at the other end. Usually, data is encoded by first generating a low-frequency wave of around 10 gigahertz, then converting it into a higher-frequency signal. The drawback is that encoding data on a 10-gigahertz signal limits the data rate to about one gigabit per second.
The Battelle team was able to better this by more than a factor of 10 using off-the-shelf optical telecommunication components. The researchers modulated data on two low-frequency laser beams, then combined the two. When these two beams combine, they create a pattern of interference that acts as a 100-gigahertz signal. "It looks as though we have a laser beam that has a 100-gigahertz frequency," Ridgway says.
Small, low-power access points boost wireless speeds indoors and in busy areas.
There are some limitations that may be worked through but make me reserved. For starters it looks like this is unidirectional, which means it will largely be used for backbones. I think we are getting ahead of ourselves with images of a dish on every roof delivering 10Gbps dancing in our heads. Next, as far as I know the higher frequency = more easily blocked by physical matter such as trees, houses, etc. This is why 2.4ghz is still favored over 5ghz in spite of the 2.4 freq. being cluttered.
This sounds great, but I think the applications will still be very limited.
@runlevelfour You're definitely right about limitations. Since the signal is sent in a point-to-point manner, it's not the sort of wireless that could work as a cellular network. That said, there are plenty of applications where cutting the cord or fiber, even in direct line of sight, could be beneficial.
Higher frequencies do not allow for higher transfer rates because they "oscillate faster." This is simply not true at all. Hey, don't you guys teach Shannon's theorem over at MIT? It's from 1949 and it is a fundamental concept in communications technology. It is just as important with modern 10 gigabit wireless technology as it was in 1949. The limit of the bits that you can pack into any given amount of spectrum is based on the modulation rate, the noise floor, and the channel bandwidth. The 60 GHz and 100 GHz bands have more speed because they allow for huge (1GHz+) RF channel bandwidth. These high frequencies don't propagate well (they are absorbed by anything) so they aren't considered highly valuable. Thus, large chunks are given away.
How and what type of modulation are they performing on the laser beam? I'm assuming that they modulate the frequency on one beam to create a beat frequency that is in the 100 GHZ neighborhood.
So, I'm curious, and I'm hoping someone can clarify for me: Are they modulating the actual frequency of the beam (i.e. the color of the laser beam) or do they use a more conventional Pulse Width Modulation approach to achieve the resultant frequency? If it was PWM, wouldn't you have to Modulate somewhere the millimeter and above spectrum anyway in order to get the right beat frequency?
Also, as far as the 10GHZ signal being up-converted to 100GHZ, since we're talking about data transmission, wouldn't it be possible to just divide the data stream and multiplex into the 100GHZ spectrum? Which is theoretically cheaper? 10 TX pairs to get 100 gigabit bandwidth or one laser setup per TX point?
Using MMW & sub-MMW for line-of-sight communication purposes has been studied for quite some time, especially in context of inter-satellite. The high power requirements are needed to offset the atmospheric, precipitation, and other propagation losses and effects. If I remember correctly, there are four useful windows: 35, 94, 120, and 220 GHz. I'm glad to finally see some investment in this area.
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camdaddy09
38 Comments
Satellite communications?
I realize this is a huge leap forward but, what about using this instead of cell towers to run our portable devices? I do realize that the thing keeping cellphone satellites back is the slow connection speeds and all the trafic coming through it at one time. It would be awesome if we could live in a world where you were never out of touch!
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gupta
7 Comments
Not so new...
The guys at Bridgewave have been at it longer.
http://bridgewave.com/products/60ghz.cfm
Finding a market in the process, and weathering the market since year ~2000... not so easy.
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adfadfa
1 Comment
Re: Satellite communications?
There is hope that it will all be able to be used by the same tower...ever heard of skype telephones??
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